Time to replace my guitar volume control?

[edvard]

I was messing about with different buffer circuits and noticed that I get a hiss/crackle around 3 and 9.5 on the dial of my Fender.
I don't think the buffer circuit is causing it, but rather helping wear to show up in the signal better.

From what I remember, audio taper pots aren't really tapered at all, but have different resistance sections tacked together internally.
re: R.G.'s article on pots:
http://www.geofex.com/Article_Folders/potsecrets/potscret.htm
So what I'm hearing is probably the joint between the two sections wearing, and the one at 9.5 is probably the junction between resistive element and terminal wearing thin.

Has anyone else experienced this?
I've been considering replacing the volume with a 1M pot and 220k tapering resistor to get a 'true' audio taper.
Anybody else tried this, and are there any concerns I should be aware of that the Geofex article didn't address?

[Mark Hammer]

Pots work because of friction.  The wiper is a piece of spring metal whose pressure maintains contact with the resistive strip.  As you move the wiper, it scrapes - to greater and lesser degrees, depending on wiper design - against the resistive strip.

Although we might like to think that a sealed pot is somehow going to remain immune to dirt for the rest of its life, the fact is that pots generate their own internal dirt, bu scraping againstthe resistive strip over the course of thousands and thousands of rotations.

In some applications (and guitar is one of them), it can often be the case that the range within which the pot does its "scraping" (i.e., the settings you most often use) constitutes a relatively narrow arc.  We have a table radio, used primarily in the kitchen to listen to the news while doing housework, that was rarely turned up above the 9:00.  The pot was absolutely fine above that, but noisy as a main street below it.

Often, the noisy spot can be eliminated by simply prying the tabs and taking the back off to clean the strip with a little cotton-tipped applicator.  Sometimes you need a bit of extra help.  Assuming the resistive strip is within certain parameters, I use this stuff - www.stabilant.com - to augment and enhance the contact between the strip and wiper.  It is not a contact cleaner.  It forms an electro-chemical conductive layer on the strip.  While it can't be built up thickly, in the land of electrons, a micron gap is like the Grand Canyon, and it may only take a nice thin layer to restore electrical continuity between strip and wiper like new.  Of course, because it cannot be built up, some pots are effectively beyond redemption, because the strip has been worn down by the wiper far too much.

The main thing is to keep in mind that pots are susceptible to exogenous (dust) and endogenous (strip scrapings) sources of grime that create momentary discontinuities in strip/wiper contact that we hear as crackly noise.

[familyortiz]

Yeah, give it a good spray cleaning with Caig Labs Deoxit or something similar. This will often fix pot issues.

[edvard]

Trouble is, I never have it anywhere near the 3 position, so I can't see how wear happens there except as the wiper passes when I turn it down.
That means to me that I have turned this guitar up and down so much (~99% of the time it's at either 0 or 10  ) that it is wearing at the joints, so to speak.
I hit it with some tuner cleaner I had hanging around, and it's better but not perfect.

[Mark Hammer]

Sometimes I find that the rivet holding the wiper contact lug is not as tight as it could be, and the wiper can be intermittent in some positions as a result.  So while the back is popped off the pot I give the rivets a little gentle pinch with the needle-nose pliers.  I find that can cure some issues.

De-oxit removes oxidation/tarnish that can impede contact, but does not remove buildup of particulate matter that has clumped (unless you really drench it).  It also does nothing with respect to any "interstitial space" that has developed between the wiper and strip as a result of erosion.  That's why someone who does professional sound reinforcement work remarked on another forum that, while he too likes Stabilant, he finds that he needs the one-two punch of application of De-Oxit and then Stabilant to be effective in rejuvenating things that can still be rehabilitated.  One cleans the contacts, and the other bridges the space between them.  This site - http://mindprod.com/bgloss/contacttreating.html - also recommends that approach.

[wavley]

Stabilant is a wonderful thing, it's great for tube sockets too!

[Mark Hammer]

I use it to "rehabilitate" switches (including stomps) and also use it to improve contact reliability in budget IC sickets.  A little poppy-seed-sized droplet on each pin and you can bring a cricuit back to life.

I got one of the elevator-repair guys in my workplace interested in it, and gave him a little half-mil "tester" vial to try out.  Most of elevator repair is electrical contacted related anyway, the way that "brain surgery" is mostly vascular surgery around the brain and not brain cutting itself.

[zombiwoof]

If the pot has an opening in the back, spray some Deoxit D5 in there and rotate the pot and see if the noise goes away.  I'm betting it will, guitar pots need to be cleaned out once in a while.  I would try this before going to more intensive solutions.

Al

[edvard]

Thanks for the cleaner suggestions, sounds like DeOxit is to be an essential on my shelf of "cans o' gunk".
At > $10 a can, it's going to have to wait a few.

Any opinions on the 1Meg + 220k idea?

[Ronsonic]

Check for DC from the buffer. When you've got a "dirty" pot and the noisy spot(s) don't move or go away with exercise, DC is the likely suspect. The DC causes a natural imperfection to sound like a fault.

If there isn't DC then it's just a flaky pot.  I try cleaning twice and if that doesn't do it, replace.

[zombiwoof]

Thanks for the cleaner suggestions, sounds like DeOxit is to be an essential on my shelf of "cans o' gunk".
At > $10 a can, it's going to have to wait a few.

Any opinions on the 1Meg + 220k idea?

I'm pretty sure they have smaller containers of D5 for less money.  Check it out.
I have a can I've had for around 20 years!.  You don't use much at a time.
Al

[twabelljr]

I use the 5oz., 5% DeoxIt D5 at work all the time. It is amazing for restoring contacts and terminals, but like Mark Hammer said, if it is worn it won't help. It is definitely worth having around if you are dealing with dirty or contaminated contacts frequently. 5oz. can on sale here for $15 quite often and will last a very long time. http://electronics.mcmelectronics.com/?N=&Ntt=deoxit. Or just replace the pot next time you re-string if no DC is present. Volume pots are cheap enough @ 2 to 10 bucks. Quote from Stewmac:

Generally, 500K-ohm pots are used with humbuckers and 250Ks are used with single-coil pickups. 25K pots are used for active systems. You can use any value you like, but a 250K will give a slightly warmer tone than a 500K pot. The 250K pot bleeds off (attenuates) some of the high frequencies to ground. A 1 Meg-ohm pot will attenuate even less than a 500K pot, so if you want to hear your guitar "wide open" you may want to try one.

I still recommend some DeoxIT with your next order.  No, I don't get paid to endorse it. Lol

[edvard]

No DC at the buffer; I just checked.
1uf cap into a PNP emitter follower; plays well with CMOS circuits where a JFET source-follower wouldn't.
Even when plugged in clean, if I listen real close I can hear it.
High gain/high impedance just brings it out apparently.

I can get a 250k Audio pot with knurled split shaft for fairly cheap just about anywhere, but maybe those heavy-duty ones from StewMac might be worth it.
I probably won't be able to hear the difference between a "real" taper and a 2-section element pot anyways.

[zombiwoof]

No DC at the buffer; I just checked.
1uf cap into a PNP emitter follower; plays well with CMOS circuits where a JFET source-follower wouldn't.
Even when plugged in clean, if I listen real close I can hear it.
High gain/high impedance just brings it out apparently.

I can get a 250k Audio pot with knurled split shaft for fairly cheap just about anywhere, but maybe those heavy-duty ones from StewMac might be worth it.
I probably won't be able to hear the difference between a "real" taper and a 2-section element pot anyways.

Two of us have suggested this, so please:
Try cleaning the pot out with cleaner (like D5), before even thinking about replacing the pot!.  You'll be wasting your time and money if cleaning is all you need, and I'd say it's quite probable that's all it does need.  This is common maintenance with pots, they need to be sprayed periodically, as the pot track wears, crud builds up in there that can cause noise.  So if you continue to play electric guitar, that can of D5 or whatever will be useful many times in the future.  You will probably have to spray the pots in your amp (and pedals) at some point, too.  Don't just automatically ditch a pot just because of a little noise.

Al

[Ronsonic]

No DC at the buffer; I just checked.
1uf cap into a PNP emitter follower; plays well with CMOS circuits where a JFET source-follower wouldn't.
Even when plugged in clean, if I listen real close I can hear it.
High gain/high impedance just brings it out apparently.

I can get a 250k Audio pot with knurled split shaft for fairly cheap just about anywhere, but maybe those heavy-duty ones from StewMac might be worth it.
I probably won't be able to hear the difference between a "real" taper and a 2-section element pot anyways.

Try cleaning, you should have a can of DeOx handy anyway. If no joy, then replace it.

In general, I don't associate StewMac with heavy duty or high quality parts. Most of their electronic stuff is pretty marginal. Maybe they've changed in the last couple of years that I gave up on them. Maybe.

[Mark Hammer]

I grow weary of writing this, but here goes...

Think of the resistive strip as being somewhat like new asphalt.  Smooth, and a joy to drive on.  Nice and silent.

Over time, several things happen.  Dirt accumulates on the road, and little bits of the surface of the asphalt get dislodged and become pebbles sitting on top.  At that point, the discontinuous contact the tire makes with the asphalt results in noise.  Part of that discontinuity noise is from stuff sitting on top of the road, and part of it is from what isn't forming the smooth surface anymore.  You could go along the road with a brrom or monster vauum cleaner, and collect/remove all the crud on top, but the road underneath would not be smooth anymore and you'd still hear noise from the discontinuity of tire/asphalt contact.

DeOxit and any other contact cleaners function to remove the crud on top.  But if the resistive strip is pitted through erosion, then you still have teeny tiny discontinuities between strip and wiper.  That's where Stabilant comes in.  It fills in the gaps, because it remains in viscous form and doesn't actually dry.  And obviously there are limits to how well it can do so, depending on how pitted and eroded the resistive strip is.  As noted, Stabilant does not dry, and as a result you cannot build up layers, like you might with conductive paint.  Its thickness is its thickness, and it the gap between any two contacts exceeds the thickness, it's new component time.

That's also why you don't apply it unless you've first cleaned off the crud from the strip with DeOxit or whatever.  Otherwise it just ends up causing the existing crud to bunch up like mud.

That's also why I tend to put Stabilant on new pots when I get them.  It acts as a sort of conductive lubricant, such that good contact is maintained without friction causing erosion of the strip.  It's the sort of stuff that, if I had a boutique pedal business, I would pretreat all my pots, and tout it as a feature, the same way people will brag that they use this brand of jack, that op-amp type, or machined IC sockets.

[edvard]

OK, OK guys, i get it!!
I KNOW how pots wear, I KNOW DC can make a pot crackly, I KNOW how oxidation, dirt and age can cause something like what I described and I KNOW that there are several products on the market that can extend the life of any given pot, OK?
OK!

Thank you one and all for the kind advice and product endorsements, but PLEASE...
Read my OP again, that's NOT what I asked about.

For the record, DeOxit costs upward of 10 bucks a can and I can get a decent pot for 2.
If I had some on hand, a few squirts and I'd be done, finis, kaput.
In fact after this thread I'm determined to save my pennies and snap up a can just for good faith.
But right now I don't, I can't, and I was just asking opinions on whether a different pot setup might work as good or better for future replacements, which WILL eventually happen, de-gunker spray or not.

NEXT time, I'll buy and use Stabilant on new pots or use DeOxit on old ones, then Stabilant, and if that doesn't fix it, I'll buy a new one.
In fact, I just might use the setup I described and let everyone know how it goes, OK?
Done.

[G. Hoffman]

Try giving it a good cleaning first.  Sometimes a bit of dust or dirt gets in there and messes with things.  If it works, great.  If not, replace the pot - but I'm guessing you'll be good with just cleaning it.


Gabriel

[twabelljr]

I was just asking opinions on whether a different pot setup might work as good or better for future replacements

That is why I posted the qoute about different pot values. I have no personal experience with different values, and that was one reference I found that "kinda" went along with your question. Please do post your results. Esp. if you change the value and/or add a tapering resistor. I would like to know what you come up with. I wish you the best in resolving your issue.

[edvard]

Yes, thank you for the quote, I always kinda new that about why the different values.
The rule of thumb was always single coil=250k humbucker=500k but I had no idea the 250k with single coils was intentionally chosen to bleed high frequencies a little more, because singles are always a little on the high side.

I will post results of any experimentation I do, but it'll have to wait until I decide this one is beyond salvage.
Actually, many times I've considered replacing my pot with a toggle switch since I hardly ever play at 5 or 7, it's always 0 or 10.
THAT oughta "open it up"...